This invention relates to a solid state image sensing device, and more particularly to a solid state image sensing device having a sufficiently high resolving power to produce a precise image.
To date, a charge transfer device (CTD) such as a charge-coupled device (CCD) has been widely accepted as a solid state image sensor adapted for a standard television system, for example, an NTSC television system. This NTSC system rules that the number of vertical scanning lines must be 512; the scanning system must be of an interlacing scanning type with one frame composed of two fields; and the aspect ratio for the TV screen must be 3:4. The number of picture elements of the CCD adapted for the standard television system, for example, interline transfer type CCD (hereinafter referred to as "IT-CCD") is chosen to have 500 (vertical).times.400 (horizontal) picture elements.
Unlike the conventional image pickup tube, a solid state image sensor such as the above-mentioned IT-CCD has excellent image pickup advantages in that it is compact, light, and quite reliable, is essentially free from pattern distortions, has less noticeable afterimage characteristics, and is completely prevented from sticking. Therefore, it is fully expected that a solid state image sensor will be more widely accepted in other fields than that of the conventional television, which includes, for example, ITV, commercial midget video cameras, and electronic still cameras replacing the present day camera using ordinary film prepared from a silver salt. When applied in the above-mentioned various fields, the image sensor must have a high resolving power for improvement of the picture quality.
For further improvement of an image reproduced by the current television system, it is necessary to realize the practical application of a high quality television system capable of presenting a large high precision picture for further use. It is reported as the result of studies on a high quality television that scanning should be made in a larger number of lines than, for example, 1125. For application to this particular technique, a solid state image sensor must have a far higher resolving power than is possible at present.
The aforementioned number of picture elements (about 500.times.400) is obviously insufficient to realize the high resolving power of a solid state image sensor, for example, of the IT-CCD type. Therefore it is contemplated to try to noticeably increase the number of picture elements. However, it should be noted that even the current solid state image sensor occupies the largest chip area among the various LSI elements. If, therefore, it is attempted to cause the image sensor to produce an increased number of picture elements, then the image sensor will become very expensive due to the enlargement of the chip size. If, on the other hand, it is tried to increase picture elements with the image sensor chip restricted to the present size, then it will be necessary to carry out the integration of picture elements with a far greater density (for example, over 4 times) than is currently applied. The method of manufacturing a solid state image sensor by such a high density integration is accompanied with great technical difficulties. Even if the manufacture is made possible due to general technical progress in the future, new problems will be raised in that the drive system of such a solid state image sensor would have a complicated arrangement, leading to a sudden increase in power consumption.